We have this situation:
One backend written with Spring.
One native Android app.
They share many of the models.
What it has been done is writing models in a package on the backend and then export it as jar in android.
On android we are using OrmLite to interact with these models on the DB. The models have their proper annotations to achieve this. On the backend we basically write raw crud queries for each model, this is getting crazy as every time we add a field we need to update all the relevant queries.
What we would like to achieve is to use another orm on the server. The problem is that server and tablet for old bad design choices have different column and table names even though the models are the same. Renaming columns and tables cannot be done because it involves too much work.
We need to get things smarter, but we would also like to avoid duplicating the models just to remap the models to a different database schema.
Do you have any idea on a smart way on how to achieve this?
Unfortunately, "Renaming columns and tables cannot be done because it involves too much work" is the best solution to have consistent and managebale code base in the long term.
For the short term, what could be smart is to use XML based configuration on the server and stick to annotations for the tablet app.
Update
You want to look at JPA specification, it defines the persistence mechanism in java. There are multiple implementation providers for it, here is the list for providers of the specificaions latest version.
I only have experience with Hibernate ORM which along with its native API also provides implementation for JPA. It has XML based configuration option in addition to annotations. You will have evaluate which provider suits your requirment.
If the annotation of ORMlite differ from JPA then you can even use the JPA annotation in the entity classes besides the ORMLite annotation. But beware this will make your entity model classes messy and you will need both your selected JPA implemantion library and ORMLite library on the classpath of entity model.
Related
I have requirements to let users create their own tables and to create their own forms dynamically inside application. One can image that there can be 3 separate tables: user_relations, user_relation_fields, user_relation_field_values. Together they can satisfy requirements. But apparently such solution is involved, each select requires lot of joins. It is easy to create tables dynamically and it is easy to create CRUD SQL statements dynamically from the set of fields which have been defined by users. I prefer to use annotations (instead of configruation XML files), therefor dynamic update of configuration files may not be necessary.
The question is - how to create ORM (JPA, Spring Repository) mapping to dynamically created tables. Is it possible dynamically create entities and insert them as part of already running application? Is it possible to dynamically create code of facelets pages and insert then in application? Is it good practice.
Lot of ERP type applications allow some kind of flexfields or extensibility features so this should be possible.
I have heard that Grails is dynamic Java with metaprogramming features maybe it is more appropriate to create such application in Grails (especially because it uses Spring and Hibernate)?
Any hints or suggestions are welcome. I guess it should be possible to do but some initial ideas would be helpful. Thanks!
I wondering why people need all this schemas, design patterns and so on. Sometimes it is better to write something from lower level. Your task is very good case. In my opinion it's better to write this module in pure jdbc/hql without mappings. It is worth to think about database type. It is not easy to implement dynamic entities in relation based database. Maybe NoSQL database will be better choice.
Here is my problem. I am using Play2 Framework right now and it's providing me with Ebean as my default ORM product. I know Java fairly well and decide to write a website using Java, but I also want to learn Go, and ultimately change my websites' backend codes to Go (Go's framework Revel). I know my data will still be there, but I will have to use a different ORM product to rewrite all the models. Will this cause a problem even though I maintain the same exact database structure?
It depends on what's your definition of 'problem'.
ORM frameworks provides facility to map database information (relational data) into OOP object. Variation exists between ORM frameworks as to what DBMS they support, default naming rule when mapping table/column name to class/field, update cascading, transaction management, cache management, SQL translation etc.
You can keep your database schema and map it using different ORM, above is just some problem you might / not encounter along the way
I'm trying to find a good way to implement a generic search API in Java that will allow my users to search the backend repository without needing to know what that backend technology is, and so that if in the future we switch vendors I can reimplement the underlying logic without needing to recode the API. The repository underneath could be a relational database or a document store like SOLR, CouchDB, MongoDB, etc... It would need to support all the typical search requirements such as wildcards, ranges, bitwise operators, and so on.
Are there any standard ways of approaching this problem?
Would JPA be my best bet? Would it do everything I need it for, including non-relational databases?
Thanks in advance!
What you need is a ORM framework like Hibernate, if you go for JPA, you need to re-invent a lot of wheel.
using Hibernate you can write the business logic for searching the backend database or repository without vendor specific implementation, and if later you need to change the backend, you can do it without affecting your existing business code implementation.
I would advice you to check the hibernate documentation for further reference
The Spring Data umbrella of projects provides a nice DAO abstraction named CrudRepository. I believe most of the sub-projects (JPA, MongoDB, etc.) provide some implementations of it.
JPA would be one of a number of implementations you would use to map your relational database to objects. It would not protect you from database changes.
I think you're looking for the DAO Pattern. What I'm doing is as follows:
Create an interface for each DAO
Create a higher level DAO implementation that simply calls my actual database specific implementation
Wire the higher level DAO implementation to the database specific implementation with Spring.
This way, no code anywhere touches database specific implementation. The connections are formed only in XML.
JPA is designed around RDBMS ... only. Using it for other types of datastores makes little sense since things likes its query language leak SQL syntax. JDO is designed for datastore agnoticity, and provides persistence to many datastores using its implementations such as DataNucleus, though not all of those that you mention.
JPA is designed around RDBMS, Hibernate is also designed for RDBMS. There are few implementations of JPA which support no-sql. Similar projects are built around hibernate to support no-sql databases. However the API itself is tuned for RDBMS.
Implemeting a DAO patterns would require you to write your own query api. Later extend the implementation when ever your data store changes.
JDO and DataNucleus is ground up designed for heterogeneous data stores. Already has support for a dozen stores ,plus RDBMS. Beauty is that the query api remains constant across the stores. JDO allows you to work with domain model and leave the storage details to implementations like DataNucleus.
Hence I suggest JDO api with datanucleus.
The below link gives list data stores and f features already available in DataNucleus
http://www.datanucleus.org/products/accessplatform_3_0/datastore_features.html
I have a java web application built on Stuts2/Google Guice/JPA. It uses hibernate as the JPA vendor. I would like to add support so it can be used on Google's App Engine. Of course I'm running into issues with the queries and mappings. Such as Many-to-Many and joins not being supported.
I'm trying to come up with the best solution for keeping my app able to be standalone. For example sin a tomcat/jetty on any database the JPA vendor supports or Google App Engine with datanucleus as the vendor.
One solution I thought of would be to use JPA for my standalone implementations and JDO for Google's App Engine. Obviously this would require me to annotate my model objects with both JPA and JDO annotations and to write another implementation for the DAO layer.
Are there any other good solutions that others have tried?
I think your approach is a good one. I think a well design architecture is the best approach. You will most likely see a lot of variance in the DAO layer. A good design would see a DAO interface, then each specific model access would have its own implementation of that interface e.g. JpaMyObjectDAO, JpaGAEObjectDAO etc. Also like you siad, App Engine has some special requirements when it comes to declaring your entity classes. Perhaps you could have different versions of the entity classes (each that conforms to its storage scheme like App Engine or Hibernate), then have a common DTO representation for your higher layers to use.
You could relocate your queries to an XML configuration. This way you can have queries for a RDBMS in one configuration and your queries for BigTable in another configuration.
Another idea is that DataNucleus is a JPA vendor as well. You could probably ease your development by making it your primary JPA vendor on both GAE and your Servlet Container. JPA vendors often times have very slight differences between what they do with their metadata and this may save you some headaches.
may i know in eclipse, is there any feature that will auto generate domain objects with all table relationship properly mapped in class?
can provide me with some reference articles on this?
You can use something like Hibernate to accomplish this
This plugin set for Eclipse called Hibernate Tools for Eclipse and ANT will do most of the work for you.
In particular it will do Reverse Engineering: The most powerful feature of Hibernate Tools is a database reverse engineering tool that can generate domain model classes and Hibernate mapping files, annotated EJB3 entity beans, HTML documentation or even an entire JBoss Seam application in seconds!
Telosys code generator does this kind of job.
It's an Eclipse plugin, it uses the database schema to create a light model
that is used to generate the Java code.
There are some predefined templates available on GitHub (for JPA, POJO, Documentation, Spring MVC, etc )
See http://www.telosys.org
and http://marketplace.eclipse.org/content/telosys-tools
Templates : https://github.com/telosys-templates-v3
Articles about code generation with Telosys :
https://modeling-languages.com/telosys-tools-the-concept-of-lightweight-model-for-code-generation/
https://dzone.com/articles/telosys-a-code-generation-tool-by-laurent-guerin
You can use Hibernate Tools 3.0.0.GA either via Eclipse or ANT to auto-generate your hibernate domain entities directly from your database tables.
See tutorial here :
http://docs.jboss.org/tools/3.0.0.GA/en/hibernatetools/html_single/index.html
I have a solution for you i.e to create auto generate domain objects with all table relationship properly mapped in class ...Try Dal4j yes you can find it in sourceforge.net/p/dal4j/wiki/ DAL4j is a Command Line and Framework tool that can be used to reverse engineer a MySQL or SQLServer database schema into a set of JPA Entity Beans.
DAL4j can be useful for scenarios where there is an existing database schema but a technology other that JPA is used by applications to interact with the database. DAL4j can provide an easy way to migrate your code base from other technologies such as JDBC or Hibernate to JPA.
The beans generated can be 1 or two types: Simple or Framework. Simple beans are standard pojo classes managed by your application using JPA semantics. Framework generated pojos use the DAL4j framework DAO generic to simplify CRUD operations.
DAL4j provides optional hooks to allow you integrate encryption/decryption of data fields that must be encrypted in the database.
Last, DAL4j provides a set of Generic classes that can be used to simplify creation of Session Beans which perform CRUD operations using generated Entities.
I think you will find this article feasible....
You want an object relational mapping of which Hibernate is the most popular for Java. The hibernate tools are typically better for taking annotated classes and using them to generate a schema, as opposed to vice versa, which is what you sound like you're doing. I suspect you'll be doing a lot of hand-annotating if you're working with a legacy DB schema.
if you use grails, you can generate domain objects with GRAG http://sourceforge.net/projects/grag
I use eclipse for java development, but when it comes to generating domain entities I use Net beans.
Create an EJB module, and then right click and generate entities.
You need to set up the database also you can select the tables you want visually.
Regards
Lyju
It feels like another rather common question that people always run into.
The link below links to a blog detailed enough for me to learn how to generate entities from database schema the first time.
http://shengwangi.blogspot.com/2014/12/how-to-create-java-classes-from-tables.html
Just in case, the following link refers to eclipse help page. This link should never expire:
http://help.eclipse.org/juno/index.jsp?topic=%2Forg.eclipse.jpt.doc.user%2Ftasks021.htm
I downloaded JBoss and failed to understand how it works. I think the plugin that I used is Hibernate Tools but I am not sure as I did not install any new plugin for this purpose. I am using Eclipse Luna for EE.
Hope this helps.
I got so tired of manually coding this kind of stuff so I made a tool to generate models, dao, and dao implementation from a schema. It's oriented towards spring boot and only tested on MySQL, but for those that don't want to use Hibernate and just want to work with jdbc/sql and JdbcTemplate, or just want POJOs with getter/setters generated for tables, then this could perhaps be something to kick off the coding.
Called Jassd (Java Automated Spring Source-code for Databases generator), I'm "jazzed" to introduce this tool: https://github.com/aforslund/jassd